Apple released Mac OS X 10.7.4 to the public back in May and we didn't expect to see another version of OS X Lion before Apple releases Mac OS X 10.8 Mountain Lion this July.
But it turns out that Apple has another iteration in the works, and they have released OS X 10.7.5 to developers.
It is generally unlikely Apple would release an incremental update to developers unless it has an important feature that they needed tested. We assume that this update is to prepare users for OS X Mountain Lion.
The update carries the build number 11G15 and is only available to developers in the Mac Dev Center. The general public will have to wait a little longer before they can enjoy the goodies which come with OS X 10.7.5 for your Mac.